A friend has a heat pump with a 80% efficient Natural Gas furnace. All of the low voltage wiring converges at a dual fuel kit that is mounted on a nearby return air duct. I have some questions about how this should work:
1) What is the purpose of the dual fuel kit?
2) Will the heat pump continue to run when the stat calls for auxilliary heat and turns on the gas furnace?
3) I understand that the outdoor unit switches to A/C in order to defrost the outside coil. On regular A/C systems, homeowners are always warned not to run them if the outside temp is cold. What is different with a heat pump that allows it to run as an A/C in very cold temps without damaging the compressor?
Thanks so much for any replies to my questions.